Synergistic analgesic composition of 1-(mu-aminophenyl)-2-pyridone and morphine derivatives



v Oct. 8, v1963 -J. F. REINHARD f Y sYNERGIsTIc ANALGEsIc coMPosITIoN oF1 ,(m-AMIN0PHENYL 2-PYR1D0NE 4, A NDMORPHINE DERIVATIVES yFileaNov, e.1961 "f2 sneets-Sngetfz AND CODEINE PHoSPHATE i THfoHETc/AL (SUMMATION)z ACTUAL (wrm .95% FlouclAL LIMITS) (ToxlclTY) so 5a 4a PERCENT oFAMPHENmoNE IN MIXTURE nooo sa o

zoo 100 forrzgs.

United States Patent O The invention relates to analgesic compositionscomprising codeine, morphine, and like analgesic morphine derivatives intheir free base form or in the form of their addition salts mixed with asubstituted m-aminophenyl- 2-pyridone as free base or the addition salt,these amino compounds having the structural formula:

in which R3, R4, R and R6 are substituents selected from l the groupconsisting of hydrogen and lower alkyl groups; and also the compound inwhich R4 is phenyl and in which the substituents R3, R5 and R6 are eachhydrogen; and wherein, in all said compounds of said groups above, R1

and R2 are substituents selected from the group which consists of loweralkyl groups, lower alkanoic acid acyl and hydrogen; and including thenon-toxic mineral acid addition salts of the aforesaid amino compounds.

Representative mixtures on which most of the experimental work wascarried out are the mixtures of codeine phosphate andl-(m-aminophenyl)-2-pyridone, the latter compound having been given thegeneric name of amphenidone.

An object of the invention is to provide an analgesic compositioncontaining codeine, morphine, or other analgesic morphine derivative,wherein the amount of morphine derivative required for analgesia issubstantially reduced by combination with a drug which brings about asynergism.

Synergism has been defined in various ways, but for present purposes thedefinition by Wells will be used (Drill, V. A., Pharmacology inMedicine, 1958, p. l2) namely, that The response to a mixture of drugsis greater than the sum of the responses to the individual ingredients.

While amphenidone was known to have analgesic, muscle relaxing, andtranquilizing properties, the use of this material with anotheranalgesic would not be warranted unless the combination with the otheranalgesic would exhibit synergisrn.

I discovered that the combination of codeine phosphate and amphenidonein the proportion of approximately 50 percent to 93 percent by weight ofamphenidone on the total drug content exhibited analgesic synergismwhich was particularly marked in the range of 75 percent to 93 vpercentamphenidone with 25 percent to 7 percent codeine 3,106,513 Patented Oct.8, 1963 Mice phosphate. Mixtures containing 95 percent and 25 percent ofamphenidone with 5 percent to 75 percent codeine phosphate showed onlyadditive efrects.

Studies were also made to determine whether the undesirable property oftoxicity was potentiated similarly to the potentiation of the desirableproperty of obtunding pain. It was discovered that mixtures containingcodeine and amphenidone in the range of 50 percent to 93 percentamphenidone with 50 percent to 7 percent of codeine, are eitherantagonistic or simply additive with respect to acute oral toxicity.

Thus the potentiation of a useful property of the above drugcombination, namely the ability to obtund pain (analgesia) is notobtained at the expense of a corresponding increase in toxicity. Indeed,in the range of -93 percent amphenidone with 10-7 percent codeinephosphate, the toxicity of the drugs in combination was actually reducedsigniiicantly below the Value expected from the summation or theirseparate activities. This dis-v covery thus enhances the overall utilityof the combinations.

The same synergistic effects are obtained with morphine-amphenidonemixtures in substantially the same proportions of drugs. The codeine andmorphine can be used in free base form or in the form of the additionsalts such as the phosphate, sulfate and hydrochloride. Likewise theamphenidone or the substituted amphenidones coming under the aboveformula, can be used as the free base or acid addition salts such as thephosphate, sulfate, or hydrochloride.

The proportions given are on the basis of amphenidone or like base andcodeine, phosphate, or morphine sulfate. They will be approximately thesame for the salts of amphenidone with the base or other salts ofcodeine and morphine.

The following gives details of the studies on combinations of codeinephosphate and amphenidone:

DETERMINATION OF ANALGESIC ACTIVITY Analgesic activity was determined bythe method of Eddy and Leimbach (l. Pharmacol. 107: 385, 1953): Adultmale mice (18-26 grams, C. F. #l strain) in groups of lil are placed ona metallic surfacemaintained at 54-55 C. In 90 percent of the normal,untreated animals pain responses (blowing on the paws and/or jumping,both hind feet leaving the plate) can be elicited within 10 seconds. Theactual range observed in a large study was 2.4 to 34,5 seconds.

Consequently, the cut-oit time was iixed at 40 seconds.

ANALGESIC ACTlViTY OF AMPHENIDONE AND CODEINE PHOSPHATE, SEPARATELYAmphenidone and codeine phosphate, suspended in 10 percent acacia, wereadministered by stomach tube to C F. No. l Iadult male mice (1S-26grams) in groups of 10 at doses ranging -from 125 to 7 50 mg./kg. foramphenidone and 25 to 125 mg./kg. for codeine phosphate. One-half hourlater (time of peak elect) the animals were exposed to the holt platelas described above, and :the numbers failing to exhibit a pain responsewithin 40 seconds were recorded as analgesic. The dose required toproduce analgesia in 50 percent of the treated animals, together withthe percent fiducial limits and chi-square were computed graphically,according to Litchfield and Wilcoxon (I. Pharmacol. 96: 99, 1949). Theresults have been summarized in Table I.

i 3 Table 1.-Analgesic Activity of Amphendone and C- deine Phosphate,Separately C ODEINE PHOSPHATE Based on the EDS@ values, codeinephosphate is shown to be 5.5 times as potent as amphenidone. Thecalculated chi-square values are less than the tabular values.

Table 2 shows the responses of both drugs, codeine phosphate andamphenidone, over a wide range of doses. Table 2.-Summaton of Ejecls ofAmphenidone and Codeine Phosphate X Y X1 Y, Percent of Amphen- CodeineAmphen- Codeine ED50 amphenidone idone idono (XH-Y1) in mixturecalcul/ated, XI X 100 mg. rg. Response: Per- Xl'l'l cent analgesic Dose'mg'lkg (calculated) 0 50 5 59 64 7. 8 0 50 10 59 69 14. 5 0 50 19. 7 5978. 7 25. 0 0 50 29. 5 59 88.5 33. 3 0 50 47. 2 59 106. 2 44. 4 0 50 5959 118 50.0 0.01 49. 99 68. 5 59 127. 5 53. 7 0. 02 49. 98 75 59 134 56.(l 0.03 49. 97 78 59 137 5G. 9 0. 05 49. 95 84 59 143 58. 7 0. 49. 9 9059 149 (i0. 4 0.20 49. 8 100 59 159 62. 9 1.0 49. 0 125 58 183 68. 3 5.045. 0 165 55 220 75.0 1D. 0 40.0 195 50 245 79. 6 12. 5 37. 5 200 48 24880. 6 20. 0 30. 0 230 42 272 84. 6 25. 0 25. 0 245 38 283 86.6 30. 020.0 265 35 300 88.3 35. 0 15.0 280 31 311 9D. O 37. 5 12.5 290 29 31990. 9 40. 0 10.0 300 27 327 91. 7 45.0 5. 0 310 21 331 93. 7 47. 5 2. 5320 17. 5 337. 5 94. 8 49.0 1. 0 325 14 339 95. 9 49. 8 0.2 325 10 33597. 0

For example, referring to the above table for a 25 percent response byboth drugs, a combination of 245 mg./kg. of amphenidone and 38 nig/kg.of codeine phosphate would be required if the drugs act by simplesummation. This would correspond to a mixture containing 86.6 percent ofamphenidone and 13.4 percent of codeine. By the same procedure, all `'ofthe various combinations shown in Table 2 have been calculated.

A theoretical curve has been constructed from the data of Table 2 (FIG.1). Values 0f 100 and 0 on the abscissa correspond to ED50s for pureamphenidone (32S) and codeine phosphate (59), respectively. Note thatthis curve is not a straight line, between these two points, as has longbeen assumed e.g. by Chen and Portman (A.M.A. Archives of Neurology andPsychiatry 68: S10-14, 1952).

Based on the conventional procedure in which 10 (ten) animals are usedper dose point a 10 percent effect, i.e., 1 (one) out of 10 (ten)animals exhibiting analgesia, would be the minimum recognizableresponse. A dose of 27 mg./kg. of codeine phosphate, or 195 mg./kg. 0famphenidone would be required tor this minimal effect. Nevertheless, inTable 2 values below these critical levels have `been computed tor thepurpose of completing the curve shown in FIG. 1. Actual doses of drugsshown in the tirst six and the last four lines of Table 2 were selectedwith reference to percentage composition of the mixtures, the activitycontribution being zero in the case of amphenidone, and essentially nilfor codeine phosphate, respectively.

The theoretical curve of summation was constructed as a frame ofreference, hence EDsos of actual physical mixtures falling clearly belowthe curve represent synergistic combinations of the two drugs.Theoretically, mixtures could show summation synergism or antagonism,depending on whether their ED50 values fell on, below, or above thecurve.

Effects of actual combinations are presented in the following section.

DETERMINATION OF SYNERGISM Seven physical mixtures of amphenidone andcodeine phosphate were prepared containing 95, 93, 90, 85, 75, 50, and25 percent of amphenidone by Weight. The ED50 of each mixture wasdetermined as described above and results have been summarized in Table3, FIG. 1 Table 3 is given below:

Table 3 .--Analegesc Activity of Amphendone- Codeine Phosphate Mixtures(1) Amphenidone 95% (2,850 mg); codeine phosphate 5% (150 mg.)

Table S-Continued (3) Amphenidone 90% (2,700 mg); Codeine phosphate 10%(300 mg.)

o/io o W10 60 135 115158 1.41 9.49 s/io 8o Synergisrn.

(1,500 mg); codeine phosphate 50% (1,500 mg.)

Synergism.

indeterminate.

From FIG. 1, it will be apparent that mixtures coni taining 95 and 25percent amphenidone showed indeterminate effects, Whereas the remainingmixtures (93%, 910%, 85%, 75%, and 50%) showed synergism. From FIG. 1expected ED50S were obtained from the theoretical curve of addition andcompared to values actually found.

Table 4, given below, summarizes the results in tabular form.

Results summarized in Table 4 reveal that the experimental values werepercent less than the values expected from summation, except for the 95percent mixture which did not show synergism.l The contribution ofamphenidone at the percent level was very little.

. CONCLUSION It is concluded:

(1) 'Ihat mixtures containing amphenidone (A) and codeine phosphate (C)in the following percentages are markedly synergistic with respect toanalgesic activity:

93% A, 7% C 90% A, 10% C A, 15% C 75% A, 25% C (2) Such mixture-s haveutility in that the amount of codeine phosphate required for analgesiawas reduced as much as 38 percent by combination with amphenidone.

DETERMINATION OF ACUTE ORAL TOXICIT'Y Test preparations, suspended in l0percent gum acacia, were administered to adult albino mice (C F. #lmales, 17-27 grams) in groups of 10 or more at doses ranging from 500 to2000 mg./kg. Signs of toxicity included depression of the centralnervous system without preliminary excitation. Specifically, thefollowing signs were noted with increasing dosage: Loss of equilibrium,muscular ilaccidity,4 -lossV of the righting reflex, surgicalanesthesia, and death within 24 hours from respiratory paralysis.Inraddition, responses to painful stimuli were reduced. rAt necropsyAthere were no gross signs of irritation or of organ pathology.Surviving animals exhibited no signs of latent toxicity. Kills weretallied after 24 hoursand the dose required for 510 percent mortality(LD50) Vtogether with 95 percent ducial limits and chi-square Wer-ecomputed graphically according to Litchfield 'and Wilcoxon (J.Pharmacol. 96:99, 1949).

a ACUTE ORAL TOXICITY OF AMPHENIDONE AND CODEINE PHOSPHTE, SEPARATELYToxicity data for each of the compounds, including LD50 values with 95percent ducial limits, and chisquare determinations for linearity haveibeen summarized in Table 5. Based on LD50 values, codeine, phosphatewas 3.3 times as toxic as amphenidone. Table is given below:

Table 5.-Acute Oral Toxicity of Amphendone and Codeine Phosphate,Separately CODEINE PHOSPHATE Table 6 shows the mortality responses ofboth drugs over a Wide range of doses. For example, for a 25 percentresponse by both drugs, a combination of 980 mgJkg. of amphenidone and340 mg./kg. of codeine phosphate would be required if the drugs act bysimple summation. This would correspond to a mixture containing 74.2percent of amphenidone and 25.8 percent codeine. All of the variouscombinations shown in Table 6 have been computed in similar fashion.Table 6 is given below.

8 Table 6.-S1lmmatz'on of Eects of Amphendone and Codeine Phosplzate X YX1 Y1 Amphen- Co- Amphen- Co- LD anllcige idene deine idoue deine(Xi-I-Yi) in mixture caleullzted l mg- E r-X Do m Xli'Y Responei11Percent se g [kg (calculated) Effects of actual combinations arepresented in the following section.

DETERMINATION OF SYNERGISM Seven physical mixtures of amphenidone andcodeine phosphate were prepared, containing 95, 93, 90, 85, 75, 50, and25 percent of amphenidone by weight. The LD50 of each mixture wasdetermined as described above and results have been summarized in Table7, given below:

Table 7.-Acute Oral Toxicity of Amphendone-Codene M xtures (1)Amphenidone 05%; codeine phosphate 5% Number Chi-square Dose dead] LD5095% limits (mg/kg.) number Percent (mg/kg.) (mg/kg.) Comment dosedCalcu- Tabulated lar 2/20 10 5/30 17 7/30 23 1,320 124.1 7.8 Non-linearsummation. 20/20 100 20/20 100 (2) Amphenidone 93%; codeine phosphate 7%48 1,625 1,464to1,804 1.6 7.8 Antagonism. l e/1o 9o (3) Amphenidone 90%;codeine phosphate 10% 1,800 1,703 t0 1,903 2.0 7.8 Antagonism' (4)Amphenidone 85%; codeine phosphate 15% g3 1, 490 1,412 to 1,572 1.6 6.osummation 9/10 9o Table 7 .-Continued (5) Amphenidone 75%; codeinephosphate 25% Number Chi-square Dose dead] LD50 95% limits (mg/kg.)number Percent (mg/kg.) (mg/kg.) Comment dosed Calcu- Tabulated lar /100 2/l0 20 8/10 80 9/10 90 1,475 1,372 t0 1,586 3. 5 11.0 Summation.10/10 100 9/10 90 10/l0 100 Amphenidone 50%; codeine phosphate 50% 0/100 i/io 1o 9/10 47 860 755 to 955 1. 2 7. 8 summation. (i/l() 60 /10 100(7) Amphenidone 25%; codeine phosphate 75% 0/10 0 2/10 20 4/10 40 510443 to 537 .7 7. 8 summation. 7/l0 70 10/10 100 It will be apparent thatthe LD50s of mixtures containing 93 and 90 percent of amphenidone tallabove the theoretical curve, indicating signiiicant decrease intoxicity; with respect to toxicity, therefore, these combinations appearto be antagonistic. The limits of error of VI Dos of the remainingcombinations coincide with the theoretical, indicating simple summationof toxicities. The theoretical curve, mentioned above, is shown in FIG.2 of the drawing.

CONCLUSON (l) Mixtures containing amphenidone (A) and codeine phosphate(C) in the following percentages are either antagonistic for simplyadditive with respect to acute oral toxicity, as shown:

95% A, 5% `C-additive 93% A, 7% C-antagonistic 90% A, 10% C-antagonistic85% A, 15% C-additive 75% A, 25% C-additive 50% A, 50% C-additive 25% A,75% C-additive (2) Since combinations synergistic with respect toanalgesic activity are included in this group, namely, 93% A, 7% C; 90%A, 10% C; 85% A, 15% C; and 75% A, 25% C, it is concluded thatpotentiation of a useful property of these drugs, namely 'che ability toobtund pain (analgesia), is not obtained at the expense of acorresponding increase in toxicity. Indeed, in two instances (93 Iand 90percent mixtures), the toxicity of the drugs in combination was actuallyreduced significantly below the value expected from summation of theirseparate activities. This discovery adds to the overall utility of `thecombinations.

The compositions of this invention have been found to be synergisticanalgesic compositions useful for labora-tory animals such as mice,rabbits, and the like. The results with such animals indicate lutilityfor humans, but the clin-ical tests on humans have not been completed.

From the tests on laboratory animals, the safe and effective unit dosefor yhumans is -30 mg. of codeine as codeine phosphate mixed with G-400mg. of amphenidone.

The following are formulae for tablets and capsules of amphenidone andcodeine:

(l) Examples of tablets are below:

Per tablet composition of Mix dry powders Nvell and then granulate witha starch paste prepared from l lb. of starch -dissolved in l gal. ofboiling distilled water. Dry at 50 C. and reduce t-o itl() granule-thenadd:

Per tablet composition of 200 mg. amphenidone Ingredient with codeine A(mg.) B (mg.)

Magnesium stearate USP 3. 25 3. 25 Starch USP to make 325 325 Compressusing 1% punch of standard ooncavity.

(Z) A satisfactory capsule can be prepared as [follows:

Per capsule composition oi 20 mg. amphenidone Ingredient with codeine A(mg.) B (111g) Codeine USP (as SO or PO salt) 15 30 Amphenidone 200 200Magnesium stearate 2. 5 2. 5 Lactose USP to make 250 250 Mix dry powderswell and encapsulate into hard shell gelatin capsule.

AI claim:

-1. An analgesic composition consisting essentially of 50 percent to 7percent by Weight 'of ia substance selected from the group consisting ofmorphine, analgesic morphine derivatives, yand their therapeuticallyuseful acid addition salts; and rfrom 50 percent to 93 percent by Weightof a m-famino compound `of the group consisting of those having theformula: i

said compound being selected from the group consisting of: (a) thecompounds in which R3, R4, R5, and R5 are substituents #selected fromthe group consisting of hydrogen and lower alkyl groups, :and (b) thecompound in which R4 is phenyl and in which the substituents R3, R5 andR6 are each hydrogen; and wherein, in all said compounds of said groups(a) and (b) above, R1 and R2 are substituents selected lfrom the groupvwhich consists of lower alkyl groups, lower alkanoic acid acyl andhydrogen; and the non-toxic mineral acid addition salts of the aforesaid9amino compounds.

2. The analgesic composition of claim l wherein the analgesic morphinederivative is codeine.

3. A therapeutic composition exhibiting synergistic analgesic effect,said composition consisting essentially of from 50 percent to 7 percentby weight of a morphine mineral acid addition salt and from 50 percentto 93 percent by weight of 1-m-aminophenyl-Z-pyridone.

4. A therapeutic composition exhibiting synergistic analgesic effect,said composition consisting essentially of from 50 percent to 7 percent-by weight of a codeine numeral acid :addition salt and from 50 percentto 93 percent by weight :of l-m-aminophenyl-Z-pyridone.

5. A therapeutic composition consisting essentially of from 25 percentto 7 percent by weight of codeine phosphate and from 75 percent to 93percent by weight of 1m-aminophenyl2pyridone.

6. A therapeutic composition exhibiting combined synergsm of analgesiaIand lowered toxicity consisting essentially of from l0 percent to 7percent codeine phosphate by weight and lfrom 90 percent to 93 percentof lrn-aminophenyl-2-pyridone.

References Cited in the tile of this patent UNITED STATES PATENTS Scudiet al. Aug. 2, 1960 OTHER REFERENCES

1. AN ANALGESIC COMPOSITION CONSISTING ESSENTIALLY OF 50 PERCENT TO 7PERCEHT BY WEIGHT OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OFMORPHINE, ANALGESIC MORPHINE DERIVATIVES, AND THEIR THERAPEUTICALLYUSEFUL ACID ADDITION SALTS; AND FROM 50 PERCENT TO 93 PERCENT BY WEIGHTOF A M-AMINO COMPOUND OF THE GROUP CONSISTING OF THOSE HAVING THEFORMULA: